GB580734A - Titanium oxide pigment production - Google Patents

Abstract

A rutile titanium oxide pigment is prepared by calcining raw hydrolized titanium oxide in the presence of minor amounts of an alkali metal compound and a water-soluble compound of aluminium, zinc, magnesium or beryllium. To an aqueous slurry of anatase raw pigment, derived from a titanium sulphate solution prepared according to U.S.A. Specification 1,504,671, may be added a solution containing a water-soluble alkali metal salt, preferably sodium or potassium sulphate or a mixture thereof in the ratio of 1 : 4 by weight, and a water-soluble salt of Al, Zn, Mg or Be, preferably aluminium sulphate, of such concentration as to give about 0.05-2 per cent. of alkali salt; and polyvalent metal salt equivalent to about 0.05-2 per cent. of the corresponding oxide in the raw pigment prior to calcination, calculated in the TiO2. After mixing, the slurry may be dewatered and calcined, preferably at 850 DEG -975 DEG C. for about 1-3 hours until substantially converted to rutile. Other alkali metal salts may be used instead of, or in conjunction with, those specified above, e.g., chlorides and carbonates of Na and K, and chlorides, sulphates and carbonates of Li, Rb and Cs, in amounts of about 0.01-20 per cent. on the TiO2 basis. Chlorides of the polyvalent metals or any compound or mixture of compounds decomposing at the calcination temperature to a relatively white oxide may be used. The amounts range from about 0.01-5, preferably 0.05-0.5 per cent., calculated as oxides and based on the TiO2. Specified salts include ammonium and alkali metal alums. Additional alkali metal salt is required to provide the proper ratio of alkali metal salt to aluminium. Raw titanium oxide derived from solutions of the chloride or nitrate may similarly be treated. The products have improved light stability. In examples: (1) anatase TiO2 prepared by hydrolysis of titanium sulphate as in U.S.A. Reissue Specification 18,854 is calcined to rutile after addition of 0.5 per cent. potassium sulphate, and aluminium sulphate equivalent to 0.2 per cent. of oxide, on the TiO2 basis. For comparison a pigment is made omitting the alumina; (2) to an anatase prepared as in (1) is added a solution containing a mixture of potassium and sodium sulphates in a ratio of 4 : 1, and a solution of aluminium sulphate, the amount of alkali salts being equivalent to 0.75, and of alumina 0.25 per cent. of the TiO2. Calcination gives a rutile product of superior colour as shown by comparison with one without alumina; (3) anatase raw pigment is prepared by adding a sulphate solution to a sol made by heating a titanium chloride solution to 85 DEG C. for 20 minutes, heating the seeded solution slowly, and boiling for 15 minutes. The washed precipitate is calcined at 975 DEG C. after adding 0.6-0.7 per cent. of mixed alkali sulphates as in (2) and 0.25 per cent. alumina; (4) anatase prepared by hydrolysis of the sulphate is calcined at 960 DEG C., wet ground and dried. The rub-out and film colours are compared with those of similar pigments after incorporating the mixed alkali sulphates or aluminium sulphate alone or both together; (5)-(7) anatase prepared as in (1) is calcined after incorporating 0.75 per cent. of the mixed alkali sulphates and zinc, magnesium or beryllium sulphate equivalent to 0.1 per cent. of the oxide. The Specification as open to inspection under Sect. 91 comprises the treatment of all forms of titanium oxide including the pre-calcined, and the use of insoluble compounds of the polyvalent metals such as the oxides, hydroxides, and carbonates. This subject matter does not appear in the Specification as accepted.